First know this: its confirmed now that private browsing mode in Firefox 42 will come with Tracking protection enabled by default. As a result, when you visit the ‘Privacy’ category in ‘Options’, you can notice ‘Use Tracking Protection in Private Windows’ being ticked.
Mozilla is now trying new designs for Private browsing page (about:privatebrowsing) and adding tracking protection tour entry point to guide users about it.
Firefox’s Private browsing page with tracking protection gets a new design
When you open a new private window in the current Firefox 42 (which is currently in Developer edition) and later versions like Nightly, you’ll notice this new design (this may change in future).
One side of the page tells usual you’re browsing privately phrase and informs user which data will be saved and which not. Other side, tracking protection status and toggle button will be shown.
In-between these, you’ll see a gray shield icon with few elements blocked in a page (those are tracking ones) with message: ‘Private Windows now block parts of the page that may track your browsing activity‘. Whenever you open a new tab in PB mode, you’ll see this design.
Testing tracking protection in Private browsing mode in Firefox
To know TP is active and working, visit a site like espncricinfo.com, you’ll see a shield icon, which on clicking says ‘Firefox is blocking parts of the page that may track your browsing’, you’ll be allowed to disable TP for that session.
Turning off Tracking Protection in Private browsing mode
While you’re in a private window, you can also turn off Tracking Protection for PB mode in browser by visiting a new tab and by clicking on ‘Turn tracking Protection Off’.